1. Technical Field
The present invention relates to a resin member that contains a thermoplastic resin and is bonded to another resin member by ultrasonic welding and a method for bonding resin members.
2. Related Art
Structural parts of automobile bodies have conventionally been formed of metal materials such as steel materials. These days, to reduce the weight of the car body, structural parts that are formed of resin materials such as fiber-reinforced resins mixed with carbon fibers (CFRPs) are coming into use. The method for joining parts made of metal materials is roughly categorized into three methods. One is outfitting joining using bolts or the like, another is adhesion using an adhesive, and the other is fusion bonding by melting metal. Also when parts are formed of resin materials, strong bonding similar to that for parts made of metal materials is necessary. In particular, in the case of parts made of resin materials containing thermoplastic resins, a welding technology in which resin materials are melted to be bonded together is counted on.
Welding is a bonding method capable of strongly bonding parts without using a third interposed object as in outfitting joining using bolts or the like and adhesion using an adhesive. Of the types of welding, ultrasonic welding can melt the resin only in a portion that is intended to be bonded locally, and therefore has high applicability, such as with no need to consider the entire shapes of the parts. However, when parts made of resin materials are bonded by ultrasonic welding, there has been a case where the resin melted at the interface remains at the interface, and consequently the control of the thickness of the interface is difficult or the bonding strength is not stable.
In contrast, in Japanese Unexamined Patent Application Publication (JP-A) No. H10-156555, there is disclosed a welding method for bracket parts in which a melting portion and a groove running along the melting portion are formed on a welding surface of a bracket part made of resin, the welding surface is brought into contact with a surface of a base material, and vibration with pressure is applied to the melting portion from the back side of the welding surface of the bracket part. In the welding method, although the molten resin that has melted out diffuses and flows into the groove and part of the molten resin flows out to the surface of the bracket part, the molten resin that has melted out is forcedly poured into the groove by a ring-like planar portion of a recess provided on the ultrasonic horn. Thereby, the melting surface of the melting portion and the molten resin that has filled the interior of the groove become substantially the same surface, and the molten resin exhibits a function as an adhesive and the bracket part is integrated with the base material by welding.
However, the groove illustrated in the welding method for bracket parts described in JP-A No. H10-156555 is a ring-like groove surrounding the periphery of the melting portion, a groove of a configuration in which grooves are further extended radially from a ring-like groove, or grooves extending radially around the melting portion. That is, in the welding method described in JP-A No. H10-156555, a margin for escape of the surplus molten resin produced at the interface during welding is ensured by providing a relatively large groove; but when the groove is too large, an area where the bonding between the parts by using resin is insufficient may occur even in the area where the molten resin flows in.
Specifically, even in the area where the molten resin flows in, when the groove is too large, there is a concern that the molten resin is not completely charged into the space between the bottom of the groove and the surface of the base material of the bonding object, and the bonding strength is not enhanced. Therefore, although the thickness of the interface can be reduced, there is a concern that the molten resin is not stuck to the mutual parts while contributing to the bonding strength.